Doug Kerr
Well-known member
We still from time to time hear that the (maximum) magnification of such-and-such a lens is x on a camera with a certain format size.
In fact, the magnification of a lens under any situation (including at maximum magnification) is independent of the format size of the camera on which it is used. (Image) magnification is defined as the ratio of the size of some feature on the image to the size of the corresponding feature on the object. The optical laws involved have no idea how large the camera frame is.
But this misunderstanding reveals a larger truth: what we are usually interested in, for example in macrophtography, is not usually magnification.
I can illuminate this by referring to the common "rule of thumb" that "real macrophotography" occurs when the (image) magnification is at least 1.0 (1:1).
Consider now a camera with a frame size of about 10" x 8". If set up for a magnification of 1.0, an entire ladies' high-heeled shoe can generally be accommodated by the frame. But that doesn't seem like macrophotography, does it?
In fact, our concern is usually what size object can fill our frame (or, said another way, what size object field corresponds to our frame size). If we want to fill 80% of the height of our frame with the image of a coin 10 mm in diameter, then:
For a frame size of 36 x 24 mm, that will need a magnification of 1.92 (1.92:1).
For a frame size of 15 x 22.5 mm, that will need a magnification of 1.2 (1.2:1).
So let's not obsess over "maximum magnification".
In fact, the magnification of a lens under any situation (including at maximum magnification) is independent of the format size of the camera on which it is used. (Image) magnification is defined as the ratio of the size of some feature on the image to the size of the corresponding feature on the object. The optical laws involved have no idea how large the camera frame is.
But this misunderstanding reveals a larger truth: what we are usually interested in, for example in macrophtography, is not usually magnification.
I can illuminate this by referring to the common "rule of thumb" that "real macrophotography" occurs when the (image) magnification is at least 1.0 (1:1).
Consider now a camera with a frame size of about 10" x 8". If set up for a magnification of 1.0, an entire ladies' high-heeled shoe can generally be accommodated by the frame. But that doesn't seem like macrophotography, does it?
In fact, our concern is usually what size object can fill our frame (or, said another way, what size object field corresponds to our frame size). If we want to fill 80% of the height of our frame with the image of a coin 10 mm in diameter, then:
For a frame size of 36 x 24 mm, that will need a magnification of 1.92 (1.92:1).
For a frame size of 15 x 22.5 mm, that will need a magnification of 1.2 (1.2:1).
So let's not obsess over "maximum magnification".